making potassium (per) chlorate

[WSM]

The reason for Swede's thread about "Bucket Cells" was that you can make a small piece of ©PVC with all the connections to it and through it and use a thin plastic bucket as a disposable cell container. A big container (say 5 gallon ) acts as a buffer to sudden temperature excursions and has a fair external surface area to allow natural convection cooling.

As photo processing dies in favour of digital media, look for components in the used lab equipment market. I've mentioned Iwaki Bellows pumps before, -They will pump up to 30% sulphuric acid for ever and do controlled flow if suitably driven.

Glass can fail by erosion in the strongly alkaline liquor of a non pH controlled cell.

 

I believe the bucket cell concept will work with a thick piece of either acrylic or polyvinyl chloride plate, used for the bucket cell adaptor (BCA). Check the bucket cell thread in this same section...

 

WSM

[PeteyPyro]

Years ago I found (and promptly lost) this page to Alan's Lab. Anecdotal and practical information on (per)chlorate cells. The comment/questions section at the bottom I found especially informative. Take it with a grain of salt.

http://www.vk2zay.net/article/63

[Pyrophury]

Thought I'd might as well give this a go and got myself an MMO anode from lasered...

 

 

Obviously too big so I cut into 3 pieces with a hacksaw and also cut 3 cathodes from a sheet of 2mm thick grade 2 Ti sheet.

 

I've also started fabricating my tubular electrode straps, also from grade 2 Ti...

 

The ends were heated until red hot and flattened in the arbor press (4 heatings and pressings), then pressed again using a 6 tonne bottle jack...

 

 

They are air-tight.

 

All the Titanium came from China, so I hope it is actually commercially pure but I'm a little skeptical.

 

Also got myself a lead dioxide anode from Alibaba...

 

 

100x100mm.

 

I'm not sure yet how I'm going to attach the electrodes to the straps, maybe Ti rivets?

[memo]

has anyone user the positive plates out of a battery as lead dioxide anode ?

[PeteyPyro]

Hi memo: Ten years ago, Alan Yates from AlansLab, replied to the same question regarding the use of lead acid cell plates. His response was as follows:

"I haven't tried a battery plate, but I have heard that it doesn't work. The plates of a modern battery are a lead grid pressed with oxide paste and various additives that will probably cause problems for a perchlorate cell.

You could try it, but I suspect the plate will rapidly fall apart, and the Sulfate and other stuff leaching out of it probably won't help the cell much. Best bet is a newly charged plate, preferably from a brand-new battery. Gel-cell plates are more fragile and likely to be exotic compared to truck or car batteries. The plates in batteries designed for deep-cycle use are more physically robust and should last longer (if such plates will work at all).

Regards,

Alan Yates."

His complete response is in the comment section for the photographs in the link for the above referenced post that I made three posts up. The link is still:

http://www.vk2zay.net/article/63

If it is feasible, perhaps others can share their positive results and their experiences with lead battery plates.

Peter

[Arthur]

In a lead battery the form of the lead oxide is not critical, it's held in place physically and any gradual loss causes loss of battery capacity. In a Lead dioxide electrode the crystal form of the lead is more critical, the hard form is used to prevent the aggressive electrolyte from stripping the oxide layer to a suspended silt on the bottom which is toxic and hard to purify.

 

Posts by Swede have mentioned his method for plating the preferred type of lead dioxide, but will now exist without pictures.

[PTFE]

This week i got the temperature probes and a voltage-meter.

 

 

They all fit in a nice box along with a time-relay and a contactor for soft-starting the Power supply without blowing the fuse. ( There will be a choke which is shorted after 1s )

(The picture was taken in a bad angle, its not that sloppy. But unfortunately one meter is not in place because one clip has broken when mounted.)

 

There is also a little switch which will later switch on a relay which will make contact between the on/off connectors on both 150A supplys to bring them in Power-on mode.

 

 

In operation one probe will monitor the inside Temp of the Power supply and the others are placed in the cell.

One at the top one in the middle and one at the bottom of the tube.

They will all fit in one Glass tube which is then filled with water.

Edited February 1, 2018 by PTFE

[Pyrophury]

I decided to spot weld my straps to the electrodes, using a spot welder I made from a microwave oven transformer...

 

 

looks messy, but the welds seem to be quite strong.

 

I tested them in a saturated salt solution, the maximum draw I was getting was just over 1 amp at 5v, but I was expecting to get more like 10-15 amps for electrodes this size. I assume it must be because of the small crocodile clips I'm using to test them?

Edited February 5, 2018 by Pyrophury

[PTFE]

I decided to spot weld my straps to the electrodes, using a spot welder I made from a microwave over transformer...

 

 

 

looks messy, but the welds seem to be quite strong.

 

I tested them in a saturated salt solution, the maximum draw I was getting was just over 1 amp at 5v, but I was expecting to get more like 10-15 amps for electrodes this size. I assume it must be because of the small crocodile clips I'm using to test them?

That looks nice would you like to share some details how you've built the welder?

 

The low Current flow could have several reasons.

First of all should your electrolyte be fully saturated.

Also has the temperature a huge impact on the current. Maybe try out insulating your cell. (higher temp>higher current)

And as you've said, the clips in useage are not good for this application, better use a steel bolt and washers to permanently connect your wire and this should give a good contact. Wrap the connections in plastic-foil to keep the corrosive fumes away.

 

If your Power supply is more than 1m away from the cell, you should use a min. wire dia. of 4mm² if closer than 1m you should be fine with 2,5mm² too keep voltage drop low.

 

It looks like you only use one Cathode, this leads to near zero Anode-Current-density on the opposide of the cathode. You should better use a cathode on each side.

Also space the Cathodes as near as possible to the Anode (5-10mm), this will lead to a high current through the cell and less waste of energy in the form of heat.

 

I hope this will help

Edited February 4, 2018 by PTFE

[Pyrophury]

That's really helpful advice, thanks.

 

That looks nice would you like to share some details how you've built the welder?

 

It's very crude, a 300W 230V MOT, 1.5m of 35mm² welding cable, copper cable lugs and electrodes. At first I tried 2 turns of cable around the tansformer but it was under powered, so I stripped off part of the thick insulation and replaced it with a layer of self-amalgamating rubber tape and was able to get one more turn, this was able to get the titanium a lot hotter.

 

And as you've said, the clips in useage are not good for this application, better use a steel bolt and washers to permanently connect your wire and this should give a good contact. Wrap the connections in plastic-foil to keep the corrosive fumes away.

 

I intend to fill the tubes with lead/tin solder and tap the ends as shown in WSM/Swedes blogs, I'd be completely lost without those resources.

Edited February 4, 2018 by Pyrophury

[Arthur]

share some details how you've built the welder?

 

 

https://www.youtube.com/results?search_query=mot+spot+welder

[PTFE]

That's really helpful advice, thanks.

 

 

It's very crude, a 300W 230V MOT, 1.5m of 35mm² welding cable, copper cable lugs and electrodes. At first I tried 2 turns of cable around the tansformer but it was under powered, so I stripped off part of the thick insulation and replaced it with a layer of self-amalgamating rubber tape and was able to get one more turn, this was able to get the titanium a lot hotter.

 

 

I intend to fill the tubes with lead/tin solder and tap the ends as shown in WSM/Swedes blogs, I'd be completely lost without those resources.

Thanks for your details

As you just want to run <50A I dont think, that your tubes must be filled.

You could calculate Voltage drops easy. Just calculate the cross-section using a Online programm, then you use the mm² you get to calculate the Vdrop as shown one or two pages ago.

When you know the Voltage you lose, you can calculate, how much Power will be lost an a Conductor.

 

If you end up with a loss of 0,5-1V it should be okay.

 

 

All in all i just want to say, i dont think that it is a matter of filling the tubes for better conductivity.

I've ran 120A @4.5V over a Ti-Strip 1,5x50mm=75mm² and it worked out.. Not nice, but it will do its job.

 

Try out rising the temp. It always gives me a hughe increase of current.

Edited February 5, 2018 by PTFE

[WSM]

Thanks for your details

As you just want to run <50A I dont think, that your tubes must be filled.

You could calculate Voltage drops easy. Just calculate the cross-section using a Online programm, then you use the mm² you get to calculate the Vdrop as shown one or two pages ago.

When you know the Voltage you lose, you can calculate, how much Power will be lost an a Conductor.

If you end up with a loss of 0,5-1V it should be okay.

All in all i just want to say, i dont think that it is a matter of filling the tubes for better conductivity.

I've ran 120A @4.5V over a Ti-Strip 1,5x50mm=75mm² and it worked out.. Not nice, but it will do its job.

Try out rising the temp. It always gives me a hughe increase of current.

 

In my experience, not filling the tubes allowed them to heat enough to give me concerns about the PVDF compression fittings they run through (in the cell lid) being compromised.

 

My first filled CP titanium leads were filled with lead-free solder (95% tin). they worked fine at roughly 30 Amps. When I stepped up the game and ran a larger cell to about 60 Amps, the leads were getting way too hot. After I filled the leads with solid copper rods (no solder or tin), they ran much cooler, about 35^oC rather than much higher than 50^oC.

 

I haven't tried solid CP titanium leads yet, but I'm considering it for larger cells. Whether or not I partially bore through them and install solid copper cores in them depends on whether the solid titanium rods get too hot or not.

 

Copper is roughly 30 times as conductive as titanium (100:3.1 according to documentation I found), so without a copper core, excessive heating at higher currents may be a problem. We'll see...

 

WSM

Edited February 5, 2018 by WSM

[WSM]

I decided to spot weld my straps to the electrodes, using a spot welder I made from a microwave over transformer...

looks messy, but the welds seem to be quite strong.

I tested them in a saturated salt solution, the maximum draw I was getting was just over 1 amp at 5v, but I was expecting to get more like 10-15 amps for electrodes this size. I assume it must be because of the small crocodile clips I'm using to test them?

 

 

Your spot welds look good. If they don't break or come apart with gentle prying, I'd recommend using them as is.

 

Also, I agree that two cathodes will work better (twice the current flow) and better electrical stress balance on the anode (greater efficiency in oxidizer production, too). Be sure to solidly connect the power leads where higher current is involved (bolting them works well for me, outside the cell, of course), and larger conductors are better. If #4 AWG gets the job done, larger conductors will work better with fewer line losses. It's a trade off between higher material costs and higher overall quality (and longevity) of your setup.

 

Good luck and share how it goes. Thanks.

 

WSM

Edited February 5, 2018 by WSM

[WSM]

Also got myself a lead dioxide anode from Alibaba...

100x100mm.

I'm not sure yet how I'm going to attach the electrodes to the straps, maybe Ti rivets?

 

I've spot welded (flattened) tubular titanium leads to the straps on my LD-on-titanium anodes, and they work well. Part of the reason is because the welded part is deep in the electrolyte and heating won't be an issue there. I also work on making the weld as solid as possible, so heating at the weld point is minimized.

 

Have fun with your projects.

 

WSM

[PTFE]

 

In my experience, not filling the tubes allowed them to heat enough to give me concerns about the PVDF compression fittings they run through (in the cell lid) being compromised.

 

My first filled CP titanium leads were filled with lead-free solder (95% tin). they worked fine at roughly 30 Amps. When I stepped up the game and ran a larger cell to about 60 Amps, the leads were getting way too hot. After I filled the leads with solid copper rods (no solder or tin), they ran much cooler, about 35^oC rather than closer to 50^oC and more.

 

I haven't tried solid CP titanium leads yet, but I'm considering it for larger cells. Whether or not I partially bore through them and install solid copper cores in them depends on whether the solid titanium rods get too hot or not.

 

Copper is roughly 30 times as conductive as titanium (100:3.1 according to documentation I found), so without a copper core, excessive heating at higher currents may be a problem. We'll see...

 

WSM

Sure they will become hot at some point but as he remarked, he will only ran his cell up to 15, maybe 20A and i was assuming his pipes are 15mmx13mm which will lead to a 175mm² Conductor which should be capable of handling currents of 20A. Otherwise you are absolutly right, if you have to carry high currents, Ti is not the best conductor.

 

The thing i want to point out is, that it's not the tube, which holds back the current in his case.. A conductor can carry much more than its supposed to.

As heating of the leads is not his problem he should invest the time he would need for filling those tubes for other things instead, unless he is going to crank up the Amps as he is progressing further.

 

You theoretically could run that many amperage over a conducter until it burns through.

 

Edited February 5, 2018 by PTFE

[Pyrophury]

 

 

Your spot welds look good. If they don't break or come apart with gentle prying, I'd recommend using them as is.

 

Also, I agree that two cathodes will work better (twice the current flow) and better electrical stress balance on the anode (greater efficiency in oxidizer production, too). Be sure to solidly connect the power leads where higher current is involved (bolting them works well for me, outside the cell, of course), and larger conductors are better. If #4 AWG gets the job done, larger conductors will work better with fewer line losses. It's a trade off between higher material costs and higher overall quality (and longevity) of your setup.

 

Good luck and share how it goes. Thanks.

 

WSM

 

Thanks! I did some test welds on some 2mm thick Ti sheets and there's no way I'd be able to pry them apart by hand.

 

I'll make some brackets out of 1mm Ti sheet so I can connect the other cathode plate.

 

For a cell vessel I was thinking of using a cylindrical glass vase 18cm dia by 30cm tall and making a lid from a sheet of PVC, should hold 5 litres with a few inches space from the lid. Or would this be too large and inefficient?

 

And what about a salt basket, seeing as I cant top up a closed cell with fresh electrolyte(without boiling away lots of water), could I use a perforated section of PVC pipe suspended from the lid which I can continually top up with salt tablets? I'm sure I've seen this done before in another thread.

 

Cheers.

[Pyrophury]

I'll try raising the temp with a fish tank heater and see what affect that has on the current, Thanks.

 

Sure they will become hot at some point but as he remarked, he will only ran his cell up to 15, maybe 20A and i was assuming his pipes are 15mmx13mm which will lead to a 175mm² Conductor which should be capable of handling currents of 20A.

 

The tubes are 12mm x 10mm.

 

As heating of the leads is not his problem he should invest the time he would need for filling those tubes for other things instead, unless he is going to crank up the Amps as he is progressing further.

 

I need a way to attach the leads anyway, I cant think of an easier way than tapping into lead/tin and screwing in a terminal post. Will 50/50 solder rods for stained glass be OK?

Edited February 5, 2018 by Pyrophury

[Fatall209]

Al rods for ... no way !

[Arthur]

 

... continually top up with salt tablets?...

 

Leaves you the problem of tracking the progress of the reaction to it's extended completion. Not hard but has to be calculated.

[WSM]

Thanks! I did some test welds on some 2mm thick Ti sheets and there's no way I'd be able to pry them apart by hand.

I'll make some brackets out of 1mm Ti sheet so I can connect the other cathode plate.

For a cell vessel I was thinking of using a cylindrical glass vase 18cm dia by 30cm tall and making a lid from a sheet of PVC, should hold 5 litres with a few inches space from the lid. Or would this be too large and inefficient?

And what about a salt basket, seeing as I cant top up a closed cell with fresh electrolyte(without boiling away lots of water), could I use a perforated section of PVC pipe suspended from the lid which I can continually top up with salt tablets? I'm sure I've seen this done before in another thread.

Cheers.

 

Hi Pyrophury,

 

The size of the cell reaction vessel (RC) will determine the speed of the total reaction, depending on the size and current draw of your electrodes. It can get a little complicated, but don't worry about that. Just run it and see how it goes...

 

What polymer material you make the salt basket out of will be decided by the temperature the cell is running at, plus the compatibility of that polymer with the corrosive environment of the cell. PVC, for instance, is rated at 60^oC and will withstand a bit more heat at one atmosphere (no pressure). CPVC up to about 90^oC, and both these materials are fine with the corrosiveness of the electrolyte.

 

If you're running your cell at the boiling point of the electrolyte (110^o to 115^oC) then PTFE or possibly also PVDF would be a better bet.

 

Good luck. Be bold, but cautious, and share your experiences with us. Thanks.

 

WSM

[Pyrophury]

Al rods for ... no way !

 

Sorry not Al, 50:50 tin/lead to fill the Ti tubes.

 

... continually top up with salt tablets?...

 

Leaves you the problem of tracking the progress of the reaction to it's extended completion. Not hard but has to be calculated.

 

Wouldn't the sodium chlorate eventually start to salt-out by keeping the chloride concentration high? Then I can estimate how much is still left in solution.

[WSM]

I'll try raising the temp with a fish tank heater and see what affect that has on the current, Thanks.

The tubes are 12mm x 10mm.

I need a way to attach the leads anyway, I cant think of an easier way than tapping into lead/tin and screwing in a terminal post. Will 50/50 solder rods for stained glass be OK?

 

You may find that fish tank heaters won't help because they're built with limiting circuitry, so you don't cook your pet fishes. The operation of the electrodes in the electrolyte, usually heat things up without any extra external help, if the current draw is high enough.

 

50:50 solder will work fine, as long as the titanium tube is perfectly sealed (to keep Sn or Pb contamination out of your cell electrolyte). Your electrical connection will depend on the physical aspects of the setup and the current it's carrying. When in doubt, a copper, clamping connector can be used on the outer surface of the filled titanium lead tube and the power lead solidly bolted to that. I'll try to find a photo of the device, if you need one. Here in the US they can be purchased in large hardware stores or electrical supply houses.

 

Regards,

WSM

Edited February 10, 2018 by WSM

[WSM]

Sorry not Al, 50:50 tin/lead to fill the Ti tubes.

Wouldn't the sodium chlorate eventually start to salt-out by keeping the chloride concentration high? Then I can estimate how much is still left in solution.

 

Theoretically, yes. I haven't done that yet, but one method to use is to run the cell at the boiling point of the electrolyte, and the boiling off of the water will naturally concentrate the NaClO₃ to where it will drop out as the solution cools to room temperature. This is the basis of a US patent that Arthur shared with me a few years ago. The setup is more complicated because of the added hazards of such a setup, but it's entirely possible to do it safely on a smaller scale.

 

I plan to try such a setup when I can get to it.

 

WSM

[Pyrophury]

What polymer material you make the salt basket out of will be decided by the temperature the cell is running at, plus the compatibility of that polymer with the corrosive environment of the cell. PVC, for instance, is rated at 60^oC and will withstand a bit more heat at one atmosphere (no pressure). CPVC up to about 90^oC, and both these materials are fine with the corrosiveness of the electrolyte.

 

I was going to use PVC/UPVC pipe and end cap, I don't intend to run any hotter than 60^oC though so it should be OK then, thanks.

 

I did test my electrodes again and increased the temp to around 60^oC, but I only got about a .5 increase, for a total of 1.5A at 5V, even with the electrodes very close together. I've also noticed places where the MMO coating has already completely worn down to the bare metal, I only tested it for less than an hour! Perhaps it's the cheap adjustable power supply I've been using?